The present invention relates to orthopedic devices for surgical treatment of bone fractures and for the prophylactic treatment of pathological bones.
Fractures of limb bones have been treated with internal fixation devices, such as plates lying on the surface of the bone, nails running inside the medullary canal of the fractured bone, or screws affixing both ends of a fractured bone together. Certain criteria should be satisfied when treating such bone fractures. These criteria include providing reasonable structural rigidity to the fractured bone, without compromising some of the strain desired to stimulate bone cells. This stability should be ensured along the longitudinal, transversal and rotational planes of the fractured bone. The device that provides the stability to the fractured bone should minimize disruption of blood supply within the bone, periosteally and intramedullarly. Ideally, the device should be as least invasive as possible to prevent the fracture site from opening. The device should also allow the use of the affected area as soon as possible, without compromising fracture stability. Potentially, the device should also allow for the use of drugs or hardware to locally treat or enhance the union process of the fracture site.
An intramedullary fixation method is a preferred traditional method of treatment for long bone fractures, since it adequately effects affixation of the bone fracture with the use of intramedullary nails, without disturbing the periosteum of the bone. The intramedullary fixation method can be accomplished in a closed manner, and the fractured bone can be functionally used (including weight bearing) during healing. The surgical approach for insertion of intramedullary nails varies slightly for each bone and is well described in the orthopedic literature. A detailed description is offered for the femur, tibia, humerus, radius and ulna in the Campbell textbook of Orthopedic Surgery. Also the Synthes Group, in its book, offers a well-illustrated description. The Nancy nail brochure offers an illustrative description of the elastic intramedullary nails currently recommended for fracture fixation in children.
There are problems associated with many of the intramedullary fixation methods, including the lack of rotation stability, collapse of the fracture site in some fracture types, and the undesired backup of nails. Furthermore, although the actual shape of the bone typically includes some degree of curvature, the intramedullary nails used to mend the fractured bone are typically straight. Still further, the intramedullary fixation method introduces interlocking screws across the nail, creating some disadvantages. Specifically, conventional intramedullary fixation nails for long bones include a rigid structure (hollow or full), that can be locked at their extremes by the addition of screws transversally applied through the bone walls and the nail itself. This additional step makes the operation longer and sometimes cumbersome, and may require necessary additional skin incisions and significant longer use of an image intensifier (X-ray). Furthermore, undesired gaps between the bone ends can originate from the screws, which are permanent unless removed in a new operation. Also, the resultant structure in certain situations is too stiff and lacks the required elasticity. In contaminated fractures, the intramedullary nails, which are metallic, may propagate the contamination through the entire canal, despite attempts at cleaning the fracture site. This may lead to and propagate bone infection.
Recent developments in the intramedullary fixation approach have attempted to address some of these problems. For example, International Patent No. WO 98/38918 to Beyar suggests three structural designs: (1) a solid metal sheet that expands in the medullary canal; (2) a meshwork structure consisting of ribs circumferentially connected at the tips; and (3) a balloon structure that is inflated once inserted into the medullary canal. The first two structures, however, are unable to provide firm support within the metaphysis of the bone. Specifically, these structures are unable to expand at their ends, because the total expansion of the structures is limited by the circumference of the diaphyseal segment of the medullary canal. The balloon structure also has limited utility because, when inflated, it disrupts the blood supply of the bone and avoids its regeneration or recovery, and is unable to adjust to changes in the shape of the medullary canal, because it has a set volume once inserted and inflated.
U.S. Pat. No. 5,281,225 to Vicenzi discloses a structure that includes a multitude of elastically deformable stems connected together by a stub. When inserted in the medullary canal of a fractured bone, the distal tips of the stems expand outward into the end of the medullary canal to anchor the Vicenzi structure within the bone. The stem, however, is affixed to the fractured bone via a transverse screw. Additionally, the Vicenzi structure is not expanded within the medullary canal and, thus, does not provide multiple points of contact with the wall of the medullary canal. As a result, the Vicenzi structure might not ensure structural stability along the transversal and rotational planes of the fractured bone.
Thus, it would be desirable to provide intramedullary devices that provide and ensure stability to a fractured bone, without hindering the normal biological processes within the fractured bone.
The present inventions are directed to intramedullary devices that provide and ensure stability to a fractured bone, without hindering the normal biological processes within the fractured bone.
In a first aspect of the present inventions, an intramedullary device employs a porous interconnection structure to facilitate expansion of the device. The intramedullary device includes a plurality of resilient spine elements longitudinally arranged to form a resultant structure. The resultant structure has a structural shaft, a first structural end, and a second structural end. One or both of the first and second structural ends are expandable and, when expanded, has a circumference greater than that of the structural shaft. In this manner, the expanded structural end or ends can firmly engage the walls of relatively large bone cavities, such as the metaphyseal or epiphyseal areas. The expanded structural end can be conveniently formed into various shapes, such as a bulbous- or trumpet-like shape. Additionally, the structural shaft can be made expandable, such that the expanded structural shaft can firmly engage the walls of long, relatively uniform cavities, such as the medullary canal.
The porous interconnection structure interconnects the plurality of spine elements at one or both of the expandable structural ends. If the structural shaft expands, the interconnection structure can interconnect the plurality of spine elements at the structural shaft. The interconnection structure can be advantageously used to provide further support to the spine elements, aid in the shaping of the resultant structure, when expanded, and/or actuate the expansion of the resultant structure, while minimizing any interruption of the biological processes within the fractured bone. The interconnection structure can be formed of a suitable structure, such as a mesh or struts, and can be variously connected to the spine elements. By way of non-limiting example, the interconnection structure can be disposed between the spine elements.
If the intramedullary device expands only at the first structural end, the spine elements can be affixed to a connector at the second structural end to ensure structural integrity of the intramedullary device, as well as to provide a convenient means of mounting. If the intramedullary device expands at both the first and second structural ends, the spine elements can be affixed to a connector at the structural shaft to ensure structural integrity of the intramedullary device. The length of the connector can be selected to provide more or less structure or column strength to the intramedullary device.
Any combination of the first structural end, second structural end, and structural shaft can be made to expand by pre-shaping either or both of the spine elements and interconnection structure. By way of nonlimiting example, the spine elements and/or interconnection structure can be pre-shaped, such that one or both of the structural ends, or all of the resultant structure, expands in the absence of an external restraining force. Or the spine elements and/or interconnection structure can be pre-shaped and be composed of a shape memory material, such as a shape memory alloy or polymer, having a shape transitional temperature, such that one or both of the structural ends, or all of the resultant structure, expands when heated to a temperature above the shape transitional temperature.
Optionally, either or both of the spine elements and interconnection structure can be further composed of a bioabsorbable material, such that none or only a portion of the intramedullary device need be extracted from the bone, when healed. If a second operation is needed, one of the spine elements can be advantageously made longer than the others to facilitate precise location of the intramedullary device after the entry portal through which the intramedullary device is inserted has healed over.
In a second aspect of the present inventions, an intramedullary device expands at opposite ends. The intramedullary device includes a plurality of pre-shaped spine elements longitudinally arranged to form a resultant structure. The resultant structure has a structural shaft, a first structural end, and a second structural end. Both of the first and second structural ends are expandable and, when expanded, have circumferences greater than that of the structural shaft. In this manner, the expanded structural end or ends can firmly engage the walls of relatively large bone cavities, such as the metaphyseal or epiphyseal areas. The expanded structural ends can be conveniently formed into various shapes, such as a bulbous or trumpet-like shape.
The intramedullary device further includes a connector that affixes the spine elements at the structural shaft to ensure structural integrity of the intramedullary device. The length of the connector can be selected to provide more or less structure or column strength to the intramedullary device. The connector and spine elements can be made of the same piece of material or, alternatively, can be made from separate pieces of material. The intramedullary device may optionally include a porous interconnection structure, which interconnects the plurality of spine elements at both of the expandable structural ends.
The first and second structural ends can be made to expand by pre-shaping the spine elements. For example, the spine elements can be pre-shaped, such that both of the structural ends expand in the absence of an external restraining force. Or the spine elements can be pre-shaped and be composed of a shape memory material, such as a shape memory alloy or polymer, having a shape transitional temperature, such that both of the structural ends expand when heated to a temperature above the shape transitional temperature.
Optionally, the spine elements can be further composed of a bioabsorbable material, such that none or only a portion of the intramedullary device need be extracted from the bone, when healed. If the intramedullary device includes an interconnection structure, this too can be pre-shaped, preferably, using the same material of which the spine elements are composed.
In a third aspect of the present inventions, one or both ends of an intramedullary device can be selectively expanded and collapsed using one or more slidable connectors. The intramedullary device includes a plurality of pre-shaped spine elements longitudinally arranged to form a resultant structure. The resultant structure has a structural shaft, a first structural end, and a second structural end. One or both of the first and second structural ends expand in the absence of an external restraining force and, when expanded, has a circumference greater than that of the structural shaft. In this manner, the expanded structural end or ends can firmly engage the walls of relatively large bone cavities, such as the metaphyseal or epiphyseal areas.
The intramedullary device further includes one or more slidable connectors disposed on the spine elements to selectively expand and collapse the resultant structure. By way of non-limiting example, if only one of the structural ends expands, a slidable connector can be configured to slide relative to the plurality of spine elements to apply or release an external restraining force to the expandable structural end and, thus, selectively collapse and expand that expandable structural end. If both of the structural ends expand, two slidable connectors can be configured to slide relative to the plurality of spine elements to apply or release an external restraining force to the expandable structural ends and, thus, selectively collapse and expand the structural ends, independently from one another.
If the intramedullary device expands only at the first structural end, the spine elements can be affixed to a connector at the second structural end to ensure structural integrity of the intramedullary device, as well as to provide a convenient means of mounting. If the intramedullary device expands at both the first and second structural ends, the spine elements can be affixed to a connector at the structural shaft to ensure structural integrity of the intramedullary device. The length of the connector can be selected to provide more or less structure or column strength to the intramedullary device. The intramedullary device may optionally include a porous interconnection structure, which interconnects the plurality of spine elements at both of the expandable structural ends.
In a fourth aspect of the present inventions, one or more ends and the center of an intramedullary device can be selectively expanded and collapsed using one or more slidable connectors. The intramedullary device includes a plurality of pre-shaped spine elements longitudinally arranged to form a resultant structure. The resultant structure has a structural shaft, a first structural end, and a second structural end. One or both of the first and second structural ends expand in the absence of an external restraining force and, when expanded, has a circumference greater than that of the structural shaft. In this manner, the expanded structural end or ends can firmly engage the walls of relatively large bone cavities, such as the metaphyseal or epiphyseal areas. Additionally, the structural shaft expands in the presence of a longitudinal compressive force.
The intramedullary device further includes one or more slidable connectors disposed on the spine elements to selectively expand and collapse the resultant structure. The slidable connector can be, for example, annular rings or sleeves. The annular rings or sleeves can have through-holes or slots circumferentially disposed on the annular rings or sleeves, through which the spine elements pass.
By way of non-limiting example, if only one of the structural ends expands, a slidable connector can be located between that structural end and the structural shaft. The slidable connector can be configured to slide relative to the plurality of spine elements to selectively collapse and expand that structural end and structural shaft. That is, when the slidable connector is slid towards the structural shaft, a compressive force is applied to the structural shaft, and an external restraining force is released from the structural end, thereby expanding the structural shaft and structural end. On the contrary, when the slidable connector is slid away from the structural shaft, the compressive force is released from the structural shaft, and the external restraining force is applied to the structural end, thereby collapsing the structural shaft and structural end.
If both of the structural ends expand, one slidable connector can be located between the structural shaft and one of the ends, and another slidable connector can be located between the structural shaft and the other of the ends. The slidable connectors can then be configured to slide relative to the spine elements to selectively collapse and expand the structural ends and structural shaft.
If the intramedullary device expands only at the first structural end, the spine elements can be affixed to a connector at the second structural end to ensure structural integrity of the intramedullary device, as well as to provide a convenient means of mounting. If the intramedullary device expands at both the first and second structural ends, the spine elements can be affixed to a connector at the structural shaft to ensure structural integrity of the intramedullary device. The length of the connector can be selected to provide more or less structure or column strength to the intramedullary device.
In a fifth aspect of the present inventions, one or both ends of an intramedullary device can be selectively expanded and collapsed using a mechanical actuator. The intramedullary device includes a plurality of resilient spine elements longitudinally arranged to form a resultant structure. The resultant structure has a structural shaft, a first structural end, and a second structural end. One or both of the first and second structural ends expand and, when expanded, have a circumference greater than that of the structural shaft. In this manner, the expanded structural end or ends can firmly engage the walls of relatively large bone cavities, such as the metaphyseal or epiphyseal areas. The expanded structural end can be conveniently formed into various shapes, such as a bulbous or trumpet-like shape.
The mechanical actuator is in communication with the spine elements to selectively urge the spine elements at the first structural end and/or second structural end inward and outward. By way of non-limiting example, the mechanical actuator can include a threaded hollow connector and a threaded rod, which is threaded within the hollow connector. If the intramedullary device expands only at the first structural end, the spine elements can be affixed to the threaded connector at the second structural end. If the intramedullary device, on the other hand, expands at both the first and second structural ends, the spine elements can be affixed to the threaded hollow connector at the structural shaft.
For each structural end that expands, the mechanical actuator includes a collar rotatably mounted to the respective end of the threaded rod, and a plurality of rigid arms hingedly mounted between the collar and the spine elements at the expandable structural end. In this manner, alternate rotation of the threaded rod in first and second directions provides umbrella-like movements to selectively expand and collapse one or both of the structural ends.
In a sixth aspect of the present inventions, an intramedullary device employs a flexible cable and a removable handle assembly to facilitate the proper positioning of the device with a fractured bone. The intramedullary device includes a plurality of resilient spine elements longitudinally arranged to form a resultant structure. The resultant structure has a structural shaft, a first structural end, and a second structural end. One or both of the first and second structural ends are expandable and, when expanded, has a circumference greater than that of the structural shaft. In this manner, the expanded structural end or ends can firmly engage the walls of relatively large bone cavities, such as the metaphyseal or epiphyseal areas. The expanded structural end can be conveniently formed into various shapes, such as a bulbous or trumpet-like shape. Additionally, the structural shaft can be made expandable, such that the expanded structural shaft can firmly engage the walls of long, relatively uniform cavities, such as the medullary canal.
The intramedullary device further includes a porous interconnection structure that interconnects the plurality of spine elements at one or both of the expandable structural ends. If the structural shaft expands, the interconnection structure can interconnect the plurality of spine elements at the structural shaft. The interconnection structure can be advantageously used to provide further support to the spine elements, aid in the shaping of the resultant structure, when expanded, and/or actuate the expansion of the resultant structure, while minimizing any interruption of the biological processes within the fractured bone. The interconnection structure can be formed of a suitable structure, such as a mesh or struts, and can be variously connected to the spine elements. By way of non-limiting example, the interconnection structure can be disposed between the spine elements.
The spine elements and/or interconnection structure are pre-shaped and composed of a shape memory material, such as a shape memory alloy or polymer, having a shape transitional temperature, such that one or both of the structural ends, or all of the resultant structure, expands when heated to a temperature above the shape transitional temperature. The flexible cable is mounted to the resultant structure, preferably, at the shaft of the resultant structure. Application of a tensile force on the flexible cable pulls the intramedullary device towards the origin of the tensile force. The removable handle assembly includes a handle and a flexible rod, which is removably disposed within the resultant structure. The removable handle assembly can be used to push the intramedullary device around tight corners, and can then be removed after the intramedullary device has been properly positioned within the fractured bone.